The present invention relates to an improvement of a tube type roller pump used for injecting, e.g., a medicinal solution, and more particularly, to a pump with improved discharge accuracy.
An apparatus of plasma pheresis that removes harmful components such as cholesterol contained in blood employs a tube type roller pump for conveying the blood collected from a donor and the blood plasma separated into blood plasma and blood cell components by a blood plasma separator. An elastic tube constituting this pump is disposable since the elastic tube is contaminated by blood and the like every time it is used. Hence, it is required that an elastic tube be attached and detached with ease.
FIG. 2 is a perspective view showing the construction of an example of such tube type roller pump. In FIG. 2, reference numeral 1 denotes a main body that constitutes a stator; and 2, a rotor that is rotated about the center P of the shaft by a not shown drive means at a predetermined velocity. Pairs of regulating members 2a are disposed on both surfaces (the bottom surface is not shown) closer to the end portion of the rotor. The regulating members 2a in each pair are arranged at an interval that is wider than the outer diameter of an elastic tube that will be described later. Reference numeral 3 denotes a roller that is rotatably fixed to each of both ends of the rotor 2.
Reference numeral 4 denotes the elastic tube. Two tube connectors 5a, 5b respectively having collars 6a, 6b are attached to the elastic tube 4 at a predetermined interval so as to be watertight. Reference characters 7a, 7b denote notches formed at a lower portion of the main body 1 so as to be distanced at a predetermined interval. Each of these notches 7a, 7b is formed to have such a width as to allow the outer diameter of the tube 4 to be inserted thereinto and the corresponding collar 6a or 6b of the tube connector 5a or 5b to be engaged therewith. Reference numeral 8 denotes a pump cover that covers the rollers 3 and the tube 4.
In the aforementioned construction the elastic tube 4 is not only interposed between each of the pairs of regulating members 2a formed on the rotor 2, but also inserted into the notches 7a, 7b, and then the collars 6a, 6b on both ends of the tube connectors 5a, 5b are retained in the notches 7a, 7b of the main body while extending the elastic tube 4 along the inner surface of the stator 1 as shown in FIG. 3 (a). In this case, the distance between the inner diameter of the stator 1 and each roller 3 is adjusted to such a value as to allow the inner surfaces of the elastic tube 4 to come in contact with each other when the rotor 2 is rotated in a direction indicated by the arrow M.
Then, when the rotor 2 is rotated with one end of the tube 4 connected to, e.g., a donor, a predetermined quantity of blood, which is (.pi.d.sup.2 /4).times.L), can be discharged every rotation of the rotor 2 (if it is assumed that the inner diameter of the tube is .phi.d, and that the length of the tube partitioned by the rollers is L (nearly equal to (distance between the shaft center P of the rotor 2 and the axis of the tube r.times..pi.)). Further, the used tube 4 is easily replaceable by removing the tube connectors 5a, 5b from the notches 7a, 7b.
Discharge of the thus constructed tube type roller pump fluctuates attributable to dimensional errors in the inner diameter of the tube and the length of the tube within the pump. Further, in the aforementioned pump movement of the connectors 5 disposed on both ends of the tube 4 is not regulated. Therefore, the tube 4 is pulled as the rotor 2 rotates as shown in FIGS. 3 (b) and (c). As a result, portions indicated by "A" and "B", for example, are separated from the inner wall of the stator 1, and one 5b of the tube connectors expands by a length indicated by "d" from the main body 1. Such expansion is also responsible for the error.
FIG. 4 shows how an exemplary discharge accuracy test was conducted using the aforementioned pump. The distance between the rollers and the stator is adjusted so that the delivery pressure of the pump was 2 kgf/cm.sup.2 or more before starting the test with the distance between the shaft center of the rotor and the axis of a tube when the tube was set along the stator being 35 mm using the tube having an outer diameter of 10 mm and an inner diameter of 6.6 mm. The test result exhibited errors up to 25% with respect to the nominal discharge that is equal to 200 ml/min.